"It turns out that their social integration scale is a really good predictor of who gets sick and who doesn't."

Beginning nearly 40 years ago, social scientists began to look deeply and regularly at the ways people related to other people--spouses, family, friends, and others--and how different people were affected by their own social networks.

What they discovered, and have consistently found in later studies, is that the diversity and numbers of our social connections are directly related to our health, happiness, and longevity. Social networks certainly include close friends and family members. But they extend outward from these intimate relationships to encompass extensive and often intricate networks of human ties that influence us in ways we may not even know.

"We would ask people, 'Are you married?' 'Do you belong to social groups?' 'Do you belong to a church?' 'Do you have friends?'" says Sheldon Cohen, a relationship researcher and psychologist at Carnegie Mellon University. "The more they have, the better off they are," he adds.

Cohen rattles off a list of the ways social ties influence our well-being: "It predicts mortality. It predicts cardiovascular disease. It even predicts the recovery rates from cardiovascular disease. It predicts the progress of cancer. It predicts cognitive function [in later life]. It even predicts the common cold."

Cohen's own research group has exposed healthy people to a cold virus after first measuring the state of their immune systems. About a third of the people get sick. "It turns out that their social integration scale is a really good predictor of who gets sick and who doesn't," he says.

Claude Fischer, a sociologist at the University of California at Berkeley, divides network relationships into three roles: providing emotional support, giving practical help, and social interaction, such as going to the ball park together. "Our relationships tend to be reciprocal over the long run, in terms of there being a balance of giving and getting," he says.

Notably, family relationships can remain significant even if they are not balanced and reciprocal. A relationship with a dominating parent, for example, can continue to be meaningful even if it's not balanced or perhaps even reciprocal. Strained or hostile relationships among family members remain significant, even though the family members may never communicate or see one another. "An underappreciated thing about networks," Fischer says, "is the extent to which ties can be a mixed blessing."

However, Cohen says networks can have a positive affect on health regardless of whether the person's experiences are positive. "Every increment in the social network is related to an improvement in your health," he says. So, 10 ties are better than nine ties, which are better than eight, and so on. "There's just something about having these many social roles that is good for you, and the more you have, the better it is."

Researchers Nicholas Christakis and James Fowler, coauthors of Connected: The Surprising Power of Our Social Networks and How They Shape Our Lives, found that social networks affect happiness over three degrees of relationships, which they call the "three degrees of influence." First come the people you know, then the people they know, and finally, the people this second group knows. Your happiness can be affected by people in all three sets of relationships, including people you do not know and likely will never meet. Likewise, you can influence people you've never met.

If people in your direct network are happy, the odds of you being happier as well will rise by 20 percent, Christakis and Fowler say. And if people in the second layer of the network are happy, the odds that you will be happier will rise by 15 percent. The happiness effect in the third degree of removal is 10 percent. The effect is not limited to happiness but can include behavioral influences. For example, if you're gaining weight, it can influence the weights of others in your network.

Weak friendships and even encounters with people you don't know can affect your well-being, according to Karen Fingerman, professor of human development and family science at the University of Texas. She has studied interactions with what she calls "consequential strangers" and found that they can make or break a person's day and influence their mood. Think, for example, of the cheerful Starbucks barista you look forward to seeing on many days.

Casual acquaintances may also provide strong benefits. "The intimate ties give you a lot of emotional support," Fingerman says, "whereas your peripheral ties may help you with new information and diversions." Fingerman cites research showing that many of us find new jobs through our weaker social ties. "The people on the edge [of our social network] are the people who have access to information and to people that you do not know."

While social networks can be extensive, our core sets of close relationships are much smaller. "We found that the average American has just four close social contacts, with most having between two and six," Christakis and Fowler say in their research.

"People's social networks tend to shrink as they get older, especially as they get into middle age," Fischer says. This can increase loneliness and have an adverse affect on health. One antidote is to seek out new community groups and volunteer opportunities.

Developing relationships has been made easier by the emergence of Facebook and other widely used social media sites. "What social media does is that it brings us more into contact with weaker ties," Fowler says.

"The online stuff takes time away not from social ties, but from things like television and sleep," says Fischer. "There is no evidence that it undercuts face-to-face social ties."

Eli Finkel, an associate professor of social psychology at Northwestern University, researches the effect of online dating services on relationships. As many as 1 in 4 romantic relationships now start online, he says, compared with less than 1 percent that were triggered 20 years ago by personal ads in newspapers.

"You now have access to profiles of a large number of potential partners that you might be interested in," Finkel says, "and that's a godsend." But he feels online dating sites are misleading people when they say they've somehow "cracked the code" and can use technology to provide users with perfect matches. Neither the profiles nor the matching technology have yet replaced the value of face-to-face meetings and social interaction, Finkel says.

In the end, successful networks provide people with three strong types of benefits, Cohen says. One is social integration--being plugged into events, trends, and experiences beyond those that directly involve you.

Second, he says, is the social support provided to one another by network members. "When you care for other people, you're motivated to take better care of yourself," Cohen observes.

Lastly, social networks can insulate or buffer people from negative events. "Having people who you think will provide you with help when you need it helps protect you from the effects of stress on your health," Cohen says. Even when the protection is perceived, such as believing someone would "have your back" in a crisis, the benefit is real.

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